Process of demagnetizing



May 24 1938. F, a DOANE 2,118,174

PROCESS OF DEMAGNETIZING Filed June 21, 1935 INVENTOR Patented May 24,1938 PROCESS OF DEMAGNETIZIN G Foster B. Doane, Pittsburgh, Pa.,assignor to Magnailux Corporation, Pittsburgh, Pa., a corporation ofPennsylvania Application June 21,

Claims.

The present invention relates to a process of demagnetizing, and moreparticularly to a proces of demagnetizing an object of paramagneticmaterial by means of an alternating electric current.

Heretofore objects of paramagnetic material, such as iron and steel,have been usually demagnetized by (1) withdrawing the article from acoil through which an alternating current is passed, or (2) placing thearticle in a coil and gradually diminishing the alternating currentflowing through the coil.

I have found that it is possible to demagnetize such articles by passingthe alternating current directly through the article and graduallyreducing such current to substantially zero, thereby obviating the useof magnetizing coils.

In the drawing,

Figure 1 illustrates diagrammatically an apparatus for carrying out theprocess; and

Figure 2 is a diagram showing the decreasing alternating currentemployed.

In Figure 1, reference numeral 1 indicates any suitable source ofalternating current, such as an alternating current generator. Thecurrent will usually be taken from a power line through a stepdowntransformer. The article to be demagnetized, such, for example, as asteel bar 2, is connected by the lead wires 3 and 4 to the alternatingcurrent generator so that the current is passed directly through thearticle. A rheostat 5 by which the current can be gradually reduced isinserted in the circuit. The rheostat 5 preferably has a sufllcientlyhigh resistance so that the current is reduced to substantially zerobefore it is broken. Such current is illustrated diagrammatically inFigure 2.

I have found that a sufliciently strong magnetic effect can be producedin the article by passing the alternating current directly through thearticle, to overcome and reverse the original magnetism in the article.The alternating current passing through the article produces magneticfluxes in reverse directions as the current goes from positive tonegative half cycles, and so on. If the current is gradually reduced,the magnetism imparted by each half current cycle, while sufllcient toovercome the residual magnetism left by the preceding half cycle,constantly grows less and less until, when the current is reduced tosubstantially zero, the magnetism is substantially destroyed.

The magnetic effect of the alternating current tends to be concentratedat the surface of the article, with the well-known skin effect.Therefore, in demagnetizing, the demagnetizing effect is greatest at thesurface. In certain processes of testing iron and steel objects forsurface de-' fects and cracks, it is advantageous to permanentlymagnetire the article by means or an 1935, Serial No. 27,757

alternating electric current in order to concentrate the magnetic fluxat the surface of the article. When this is done, it is advantageous toemploy the present alternating current method of demagnetizing thearticle, since the maximum demagnetizing at the surface can be securedwith a minimum of current.

Instead of a rheostat, an induction regulator or a variable choke may beemployed to reduce the current.

While I prefer to use an alternating current for demagnetizing, it ispossible to use a reversing current passed through the object which isgradually reduced in strength. For example, a direct current may bepassed through the object in reverse directions by means of a suitablecurrent reversing mechanism, and the strength of the direct currentgradually reduced. The action in destroying the magnetism is similar tothat of an alternating current. When I speak of a reversing electriccurrent I intend to include not only an alternating current, but also adirect current which is periodically reversed in direction.

While I have specifically illustrated and described my process and thepreferred way of carrying it out, it is to be understood that theinvention is not so limited but may be otherwise embodied and practicedwithin the scope of the following claims.

I claim:

1. The process of demagnetizing an object of magnetic material, whichconsists in passing an alternating electric current directly through theobject, and gradually reducing the strength of the current tosubstantially zero.

2. The process of demagnetizing an object of magnetic material, whichconsists in passing directly through an object an electric current ofthe character and effect of an alternating current and graduallyreducing the strength of the current to substantially zero.

3. A method of demagnetizing an article which consists in causing analternating current to traverse the article, and gradually reducing themagnitude of the current substantially to zero.

4. The method of demagnetizing an article of magnetic material,including passing a direct electric current through the article itself,frequently reversing the direction of flow of the current, and graduallyreducing the magnitude of the current substantially to zero value.

5. The method of demagnetizing an article of magnetic material,including establishing the naked article itself as an integral part ofan electrical circuit, passing a current of the character and effect ofan alternating current directly through the article, and graduallyreducing the magnitude of the current substantially to zero value FOSTERB. DOANI.

